1. Field of the Invention
The present invention relates to a viewing optical instrument such as a telescope which is provided with an image stabilizer for stabilizing the vision in the viewing optical instrument subjected to hand movement.
2. Description of the Related Art
A telescope, which may be a monocular telescope or a binocular telescope, that is provided with an image stabilizer having a vibration compensation function is well known. The image stabilizer prevents the telescope vision in the telescope from shaking due to hand movement or the like to provide shake-free viewing and minimal eye fatigue.
In such type of conventional telescope, the image stabilizer prevents the telescope vision from shaking in general, both in the horizontal and vertical directions. Therefore, with the image stabilizer being turned ON, when the telescope is panned horizontally so as to keep track of an object (e.g., a bird) which is initially still but starts moving right or left in a horizontal direction, the image stabilizer operates to compensate the shaking of the telescope vision (hereinafter referred to as "image shake") in the direction opposite to the panning direction to reduce the image shake, which causes the motion of the telescope vision to deviate from the panning motion, possibly resulting in the user of the telescope noticing incongruity in the telescope vision while panning. Subsequently, if the moving object suddenly changes to move in the reverse direction and the user thus pans the telescope accordingly to keep track of the object in the same direction, the image stabilizer again operates to compensate the image shake in the direction opposite to the panning direction, which causes the object image to substantially deviate from the telescope vision at the time of panning. Thereafter, the moment the user stops moving the telescope upon the stoppage of the object, the telescope vision slightly moves or shakes even though the telescope is no longer in motion because the image stabilizer is still operating for initializing the stabilizing system upon the stoppage of the telescope. Obviously, with this type of stabilizing system, the image stabilizer operates against the user's intention when he or she intentionally moves the telescope in the horizontal direction. Consequently, if the user desires the image stabilizer to stabilize the telescope vision in the vertical direction while the user pans the telescope in the horizontal direction, the user must tolerate the incongruous motion of the telescope vision in the horizontal direction. This problem also occurs when the telescope is panned vertically. Accordingly, in any conventional telescope having an image stabilizer, it is sometimes the case that the user of the telescope notices incongruity in viewing the telescope vision during the use of the telescope.
Conventional viewing optical instruments provided with an image stabilizer tend to be bulky and heavy because they are designed to compensate image shake in all directions. However, in a binocular, for example, image shake tends to occur mostly in the vertical direction. This is because the wrists of the user with the binocular being held by both hands tend to move in forward and rearward directions and that the binocular can be stably held easily since the binocular is usually held by both hands with both eyepiece positions of the binocular being pressed against respective portions of the face of a user around his or her eyes. Specifically, when the binocular is used by a skilled user, little image shake in horizontal direction occurs. In this particular case it is unnecessary for the image stabilizer to be provided with a vibration compensation function for compensating image shake in the horizontal direction. However, depending upon the difference in the way the individual user holds the binocular, and also the conditions of use, image shake may often occur in the horizontal direction but hardly occur in the vertical direction. Namely, in conventional viewing optical instruments provided with an image stabilizer, it can be said that for some users and/or under specific conditions of use, the image stabilizer unnecessarily operates to compensate an image shake in a specific direction.